[Patent Literature 1] JP 2003-97756 A
Patent Literature 1 describes an electromagnetic spool valve in which the space gaps facing both the sides of the plunger in the axial direction each communicate with a drain space via an oil drain passage inside of a spool. The spool valve combines a spool valve and an electromagnetic actuator in the axial direction, and has an oil drain passage (passage hole along the axial direction), which communicates with the drain space, in a central part of a spool. The space gaps facing both the sides of the plunger in the axial direction communicate with the drain space via the oil drain passage formed inside of the spool.
The technology of Patent Literature 1 describes a respiration-use passage, which leads drain oil from the oil drain passage to a high magnetic flux density portion, being provided as a straight passage hole extending along the axial direction. The high magnetic flux density portion is one of the space gaps adjacent to both the sides of the plunger in the axial direction and exhibits a high magnetic flux density so as to give magnetic attraction power to the plunger. The movement of the spool valve therefore causes the oil (discharged drain oil) to discharge to the oil drain passage and then reach the high magnetic flux density portion smoothly; this permits foreign matter contained in the drain oil to also reach the high magnetic flux density portion easily.
Since the high magnetic flux density portion provides the high magnetic flux density, the portion tends to receive influence of the foreign matter. The foreign matter reaching the high magnetic flux density portion may involve slide abrasion or slide defect in the plunger.